“It was my first big movie, and I like to focus on the material rather than the names involved,” explains the 30-year-old standup from Queens. “I was pretty shocked when I finally saw it was Scorsese and Leo (DiCaprio). I got really nervous.”

He also got the part, playing “an asshole stockbroker,” thanks to his comedy and ad-lib abilities.

“Scorsese wanted actors who are funny and can improvise, but I have no idea if it’s a comedy,” he says of the experience. “None of us could gauge the tone when we shot it, and Scorsese’s so casual. He would actually come on set and go, ‘What do you guys think we should do in this scene?’ And we’d be, ‘Oh, you don’t have anything planned?’ So we shot all this crazy, wacky stuff for seven months, and I have no idea how it’ll all cut together.”

Rothbart was exposed to standup from an early age. His father started taking him to comedy clubs when he was just 12. “Later, at college, when I was super-depressed, I tried standup,” he recalls. “I was terrible, but I’d read that performing was good training if you wanted to write and direct, which was my main goal then, so I just kept going.”

His perseverance paid off. As a standup, he has recently done “The Tonight Show With Jay Leno,” “Conan” and “The Late Late Show With Craig Ferguson”; will appear in Comedy Central’s upcoming “Adam DeVine’s House Party”; and just co-directed his first documentary, “Hungry,” about the “weird world” of competitive eating.